The overall objective of this project is to explore the potential of nuclear magnetic resonance for providing detailed information about the structures and dynamic properties of enzymes, particularly those of high molecular weight. Enzymes specifically labeled with 13C or 19F nuclei will be obtained by in vivo incorporation of labeled amino acids or by in vitro chemical modification of intact enzymes with labeled reagents. Carbon-13 and 19F nuclei were chosen because their wide chemical shift range and the relative narrowness of their nmr signals should result in high resolution spectra. The labeled enzymes and their noncovalent complexes with substrates, inhibitors, and coenzymes will be studied by pulsed nmr techniques. The enzymes to be studied include E. coli alkaline phosphatase containing 4-fluorotryptophan, m-fluorotyrosine or (gamma-13C)-histidine, horse liver alcohol dehydrogenase amidinated or guanidinated with a 13C enriched or 19F containing reagent, E. coli tryptophan synthetase alpha subunit with 13C enriched histidine or cysteine residues, and E. coli aspartate transcarbamylase labeled with 13C in phenylalanine, tyrosine, histidine, cysteine or tryptophan side chains. BIBLIOGRAPHIC REFERENCES: Douglas T. Browne, Elaine M. Earl, and James D. Otvos, "Selectively Enriched (gamma-13C)-Histidine as a Nuclear Magnetic Resonance Probe of Enzyme Struture and Function. Synthesis and Incorporation into E. coli Alkaline Phosphatase", Biochem. Biophys. Res. Commun., in press (1976). Douglas T. Browne and James D. Otvos, "4-Fluorotryptophan Alkaline Phosphatase from E. coli: Preparation, Properties, and 19F Nmr Spectrum", Biochem. Biophys. Res. Commun., 68, 907 (1976).